... Medical use: The substance loosely called selenium sulfide (approximate formula SeS2) is the active ingredient in some anti-dandruff shampoos.[72] The selenium compound kills the scalp fungus Malassezia, which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus.[73]

Nutrition: Selenium is used widely in vitamin preparations and other dietary supplements, in small doses (typically 50 to 200 micrograms per day for adult humans). Some livestock feeds are fortified with selenium as well …

Potential of antioxidant supplements to damage health: There is evidence that antioxidant supplements promote disease and increase mortality in humans.[99][100] It was previously proposed on a hypothetical basis that free radicals may induce an endogenous response culminating in more effective adaptations which protect against exogenous radicals (and possibly other toxic compounds).[101] Recent experimental evidence strongly suggests that this is indeed the case, and that such induction of endogenous free radical production extends the life span of Caenorhabditis elegans.[102] Most importantly, this induction of life span is prevented by antioxidants, providing direct evidence that toxic radicals may mitohormetically exert life extending and health promoting effects.[99][100]